The present invention relates to an image forming apparatus, and more particularly, to a circuit that will print data in its original size when the resolution of the data received from a host computer does not match the image forming apparatus' primary resolution.
A laser beam printer, as an example of the image forming apparatus, may generally be classified, for example, as a 300 dpi (dots per inch) laser beam printer or a 600 dpi laser beam printer. A 300 dpi laser beam printer comprises a 300 dpi video controller and a 300 dpi laser beam printer engine. A 600 dpi laser beam printer comprises a 600 dpi video controller and a 600 dpi laser beam printer engine. The 300 dpi laser beam printer can print data in 300 dpi after receiving a document written with 300 dpi from a computer. Meanwhile, the 600 dpi laser beam printer generally prints as 600 dpi after receiving a document written with 600 dpi from the computer. Occasionally the 600 dpi laser beam printer will receive a document written with 300 dpi from the computer. In such a case the video controller of the 600 dpi laser beam printer transmits data of 300 dpi to the 600 dpi printer engine, and the frequency of a video clock given and taken between the video controller and the printer engine become equal. Accordingly, the size is reduced by one-half in width and length, respectively. The resulting area becomes a quarter of the size of an actual area thus causing much inconvenience in such a use.
To print the video data of 300.times.300 dpi as the original size without the above-mentioned problem, the video controller receives data of 300.times.300 dpi from the computer, and during data processing, or after finishing the data processing, enlarges the video data. Enlargement is performed according to a software method by doubling the data's width and by doubling the data's length in a memory of the video controller. Video controller 100 then receives a horizontal synchronizing signal H.sub.-- SYN and a video clock V.sub.-- CLK from an engine part 200 before transferring the video data for printing by the engine part 200. Video controller 100 then serially transmits the video data to the engine part 200, and synchronizes to the signals. Thus, the engine part 200 can print the data of 300 dpi in the original size. However, a problem remains in such a method. That is, in a case where the engine speed is slow, there is no problem in printing the video of 300 dpi according the software enlargement, but in a case where the engine speed is quick, there is much restriction.